Electrophoretic display media are generally characterized by the movement of particles through an applied electric field. These displays are highly reflective, can be made bistable, can be scaled to large areas, and consume very little power. These properties allow encapsulated electrophoretic display media to be used in many applications for which traditional electronic displays are not suitable. While bichromatic electrophoretic displays have been demonstrated in a limited range of colors (e.g. black/white or yellow/red), to date there has not been successful commercialization of a full-color electrophoretic display. One reason for this failure of commercialization is the lack of a method of manufacture that is efficient and inexpensive.
One traditional technique for achieving a bright, full-color display which is known in the art of emissive displays is to create display elements that are red, green and blue. In this system, each element has two states: on, or the emission of color; and off. Since light blends from these elements, the overall display can take on a variety of colors and color combinations. In an emissive display, the visual result is the summation of the wavelengths emitted by the display elements at selected intensities, white is seen when red, green and blue are all active in balanced proportion. The brightness of the white image is controlled by the intensities of emission of light by the individual display elements. Black is seen when none are active or, equivalently, when all are emitting at zero intensity. As an additional example, a red visual display appears when the red display element is active while the green and blue are inactive, and thus only red light is emitted.
This method can be applied to bichromatic reflective displays, typically using the cyan-magenta-yellow subtractive color system. In this system, the reflective display elements absorb characteristic portions of the optical spectrum, rather than generating characteristic portions of the spectrum as do the elements in an emissive display. White reflects everything, or equivalently absorbs nothing. A colored reflective material reflects light corresponding in wavelength to the color seen, and absorbs the remainder of the wavelengths in the visible spectrum. To achieve a black display, all three display elements are turned on, and they absorb complementary portions of the spectrum.
However, such techniques require that the colored display elements be deposited onto a substrate in substantially equal proportions aligned with the proper addressing electrodes. Failure to achieve either substantially equal proportions of colored display elements or failure to achieve registration of the display elements with the addressing electrodes results in a color display that is unsatisfactory.